I'm still very early but it's basically never efficient to put pops into stuff like cooking or smelting. maybe I just need a way larger economy of scale, but the marginal rate is always better just putting that pop into extraction directly. I guess once I'm in the dozens or hundreds the diminishing returns will take care of that, but I haven't hit that wall yet.
Hey, it does depend on the stage of the game. Also sometimes stuff that is not very population efficient could be quite resource-consumption efficient, so it's a back-and-forth kind of thing.
The furnace starts off a bit weak, but after you upgrade it, it becomes much better.
Overall boosters are very powerful, especially later on.